The determination of vehicle mass is important to the efficient operation of today's vehicles, especially in the heavy-duty commercial and industrial truck industries. For example, mass can be a selection criteria for proper gear changing control in a transmission having staged gears. Vehicle mass may also be used by various vehicle controllers in anti-lock brake systems, intelligent vehicle/highway systems and fleet management systems, to name a few. In addition, vehicle mass can be useful in speed control systems, such as for use with a cruise control system. One problem with using vehicle mass as a control parameter is that it varies with vehicle loading and is usually difficult to predict with certainty, especially with respect to heavy-duty trucks. For example, a dump truck can have a mass when loaded up to ten tons greater than when empty. In the case of a semi-tractor with a trailer, the mass when loaded can be up to 40 tons greater than when empty.
Because the mass of a particular vehicle may vary greatly, a means for accurately measuring actual vehicle mass when the vehicle is in operation is required if the dynamic vehicle mass is to be used as a control parameter. Thus, if the mass parameter is fixed at a particular value in the control system, then the various control features described above will not allow for optimal vehicle performance under all types of load conditions.
Various methods of measuring vehicle mass have been the subject of prior patents. In U.S. Pat. No. 5,490,063 to Genise, a method for determining vehicle mass as a function of engine output or driveline torque, vehicle acceleration, and the currently engaged gear ratio is disclosed. For this method, Newton's law is used directly with acceleration and force values determined from the torque and gear ratio input to estimate vehicle mass. Likewise, in U.S. Pat. No. 4,548,079 to Klatt, a method is disclosed for determining vehicle mass directly using engine output torque values and acceleration values.
Vehicle acceleration is typically computed from either engine or vehicle speed data. However, one of the problems associated with the collection of speed data is that speed signal is typically very noisy. When vehicle acceleration is used to determine the vehicle mass, the noise problem is even more significant. In order to determine acceleration, it is often necessary to measure the increase or decrease in speed values at very close time intervals. This differentiation in speed values at close time intervals causes the acceleration signal to be buried in the noise of the speed signal. Inaccurate determinations of vehicle acceleration and a correspondingly inaccurate determination of vehicle mass may result. The various controllers relying on an accurate vehicle mass determination may in turn perform ineffectively and inefficiently.
What is therefore needed is a technique for estimating vehicle mass that addresses the foregoing shortcomings. Such a technique should provide reliable, accurate estimates of vehicle mass. The method should also effectively address the problems created by the inherent noise contained in speed signal data. The technique should also be inexpensive to implement, and be readily integratable into existing vehicle control systems.